This invention relates to devices and methods for monitoring cardiac pumping, and more particularly to a new device and method for noninvasively detecting the quality of cardiac pumping resulting from cardiopulmonary resuscitation (CPR) or from automatic external defibrillation.
CPR is a well known and valuable emergency procedure for reviving a person suffering cardiac arrest. When the heart stops pumping blood, the resulting lack of fresh oxygen to the brain can cause brain damage within minutes and death can soon follow. CPR involves repetitive chest compression coordinated with mouth-to-mouth breathing, and its effectiveness depends on coordinated delivery of adequate chest compressions and rescue breaths and, to a large extent, on the quality and timing of the chest compressions. Much attention has been devoted to the subject and particularly to techniques for training emergency medical personnel as well as ordinary citizens how to perform CPR properly even under stress associated with treating a life-threatening condition and even if fatigued from a sustained effort.
A pressure-sensitive chest pad has been proposed as a feedback tool for a rescuer administering chest compressions during CPR. For example, an automatic external defibrillator (AED) recently introduced by Zoll Medical Corporation, the Zoll AED PLUS, is available with a chest pad with which it is said to monitor rate and depth of chest compressions when the rescuer presses on the pad. Voice and visual prompts encourage a compression depth of 1½-2 inches. However, the AED gives no indication of the effectiveness of pumping of blood. One of the rescuers is prompted to check the victim for the presence of a pulse or other signs of circulation such as normal breathing, movement, coughing or color of the lips or skin. Such methods do not give the typical human rescuer feedback fast enough to enable the rescuer to vary the style of chest compression in order to optimize blood pumping.
Perfusion monitors designed to measure blood gases, such as the monitor proposed in U.S. Pat. No. 5,579,763 to Weil et al., can take minutes to respond and thus also fail to provide sufficiently rapid feedback, e.g., beat-by-beat feedback, for a typical human rescuer.
A need exists for a simple and practical device which can give a positive indication of the effectiveness of blood pumping in response to chest compression during CPR. There is also a need for a simple and practical way to noninvasively detect cardiac pumping following defibrillation with an AED.
Electromechanical dissociaton (EMD) is a condition in which the R waves of the ECG either do not produce ventricular contractions or produce extremely weak contractions, resulting in little or no blood pumping. The condition is sometimes known as pulseless electrical activity (PEA). It occurs frequently because ventricular fibrillation is often not treated with CPR for a period of time or the CPR is inadequately performed. In such situations, the heart muscle, being deprived of oxygenated blood because there is no blood pumping, becomes injured and consequently beats weakly or not at all after successful defibrillation. Thus, even though an AED may indicate that the criterion for successful defibrillation has been met, namely abolishing the high-frequency fibrillation waves in the ECG, the heart muscle cannot respond adequately to the resulting R waves and the victim is likely to die as a result if other intervention is not promptly provided.
Another postdefibrillation situation for failure of the ventricles to contract is atrioventricular (A-V) block. A-V block is not uncommon immediately after successful ventricular defibrillation and no ventricular pulses are produced.
The appropriate therapy for EMD and A-V block is the prompt application of effective CPR.